# CFM question



## cion (Mar 18, 2015)

Hello fellas! I'm about to start my cigar room in my house this week. I'll make a separate thread with photos later. My question is regarding ventilation. If I use an exhaust fan at 1000 cfm, how much air (CFM wise) should my return be?

If pulling out 1000, should I bring in 1000?
Should I bring in less and create negative pressure? 
Should I have just an open air return vent (non forced air) with duct heater and allow the exhaust fans to pull in air from there as needed?
Or should I have forced air through return via fan pushing cfms back in room?

Thanks in advance for your help.


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## quo155 (Aug 10, 2010)

There are a lot of different variables to any room (also, your location/climate zone/square or cubic footage of the room, etc), and without such information...I can only offer you this: Whatever you do, you want the pull _from_ the room to be just over what is being fed _into_ the room. Yes, a slightly negative pressure.

Example, If your room is receiving 1000cfm, then you'll want to "return" (I would not put an actual return register in this room, I'd only use an exhaust fan (vent to the outside) capable of pulling the number needed), or pull out about 1050cfm+. There's no exact science to the return numbers for cigar smoking, but another example: if you only need 250cfm for the room, I'd suggest 260cfm+ in return. Now, unless you have an adequate filter system (specifically for smoke removal, etc.) in place for the return...again, I'd not return the air from the smoking room to the unit, it would then be fed into the rest of the home.

That is the simplified solution and it'll work if set up correctly.

_Fine print: I'm an Architect & MEP Engineer by trade...but this is just a suggestion!_


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## StogieNinja (Jul 29, 2009)

Tommy, I have a room thats 10Wx12Dx10H. Do you think a 300CFM fan would be enough to keep the smoke moving with say 3-5 guys in there at a time? 

As far as air, the door to the garage would have about an inch of open space for air to flow into the room, but nothing forced in... is that enough?


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## cion (Mar 18, 2015)

Thank you Quo155, please let me give you a little more info so you can possibly answer the question as proficiently as you can. Thank you BTW.

The home the room is being built is in North NJ so it gets cold in the winter. Its my recreation room. The space I'm using is approximately 270 sq feet.

Doing the calculation for CFM I was given a number of 300 cfm however I know I'll need more than that especially if I have up to 5 smokers. 
I was thinking 1500-1700 cfm exhaust pulling from two ceiling vents straight out of the house. I'm separating the hvac of my house and this room (not using dampers). So I have a few questions:

1. Is 1500-1700 cfm overkill? I'm using a speed regulator to adjust output depending the amount of smokers.

2. If I'm using that amount of cfm on exhaust, for fresh air, what should I do?

● Use no force air return, and allow the air to be pulled in naturally from the exhaust fan pulling OUT the air? (From negative pressure)

● Buy a fan (what cfm?) for air intake to PULL fresh air in from outside?

● Should I buy a duct heater? - The room will have 2 baseboard heaters as well as the fake fireplace heater.

● I've seen photos of the exhaust and fresh air intake side by side on the outside of the house in others cigar room. Doesn't that defeat the purpose of a fresh air intake? Wouldn't the intake pull the cigar smoke from the exhaust right back in?

I was going to have my exhaust and fresh air intake on opposite sides of the house.

EX








If you suggest both a fan to pull in fresh air AND a duct heater, will the heater warm the air as fast as the fan is pulling it in? Other words...how do you pair the two? (A intake fan and duct heater)

Lastly...Air conditioning.

I'm thinking of going portable AC and connecting it to the return duct for fresh air to the AC unit. I'm not sure about the best way to do AC on a small budget so if you guys have any suggestions let me know. There is no windows in or near the room.

Thanks!

Didn't mean to ask so many questions at once, but it's all HVAC related and I need to start my purchases ASAP. We're starting demolition on a couple of walls and ceiling this sunday.


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## Bizumpy (Nov 14, 2014)

If you only use an outflow fan and have an intake duct that's slightly smaller diameter than the outflow duct, you should automatically create negative pressure in the room.


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## cion (Mar 18, 2015)

Bizumpy said:


> If you only use an outflow fan and have an intake duct that's slightly smaller diameter than the outflow duct, you should automatically create negative pressure in the room.


Thanks! If I go this route then all I would need is a duct heater in the intake duct, correct?


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## Bizumpy (Nov 14, 2014)

Yes, and if the heater disrupts the flow of intake air enough, you won't even need a smaller duct to create the negative pressure.


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## quo155 (Aug 10, 2010)

Aninjaforallseasons said:


> Tommy, I have a room thats 10Wx12Dx10H. Do you think a 300CFM fan would be enough to keep the smoke moving with say 3-5 guys in there at a time?
> 
> As far as air, the door to the garage would have about an inch of open space for air to flow into the room, but nothing forced in... is that enough?


Hey Derek, 300cfm is spot on for a normal room, for your area. And, if you're not feeding anything into the room (other than from under the door), that should work fine. However and if possible, I'd shoot for a 310cfm or 320cfm, just to get more out and help fresh air enter the room from under the door.


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## StogieNinja (Jul 29, 2009)

Thanks man. I'm looking at a Panasonic Whispersync. It's DC so you can't use a dinner switch on it. 

I may end up just putting two 200cfm in instead, so I can run one or both depending on how many people are in the room. Any thoughts there?


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## quo155 (Aug 10, 2010)

cion said:


> Thank you Quo155, please let me give you a little more info so you can possibly answer the question as proficiently as you can. Thank you BTW.
> 
> The home the room is being built is in North NJ so it gets cold in the winter. Its my recreation room. The space I'm using is approximately 270 sq feet.
> 
> ...


Hey Cion! For your room size and location, I'd shoot for 700cfm exhaust, minimum.

1. The 1500+ really is overkill, IMHO and I'd keep it between 700cfm and 900cfm...as long as the number is more than whatever you decide to feed into the room. A speed regulator is a great idea!

2. 675cfm is about right for fresh air, as long as the number is less than your exhaust. It doesn't sound like you'll need a duct heater as you'll have plenty from other sources. If you're not supplying the room from your main system, then I would use a fan to pull from the outside, in...672cfm.

Portable AC's can work in your area (not here where I live!) and you can get a decent EdgeStar unit that does not require a window, you can install it with the supplied ducts to a wall with vents. It pulls air from the outside and from the inside. They're not real efficient at cooling down here but reviews say they work in your area. They are also a great dehumidifier, as a bonus...if even needed where you are. They run around $500-$600.

Whatever route you decide to go, I hope this info helps some...


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## Johnpaul (Aug 15, 2011)

Aninjaforallseasons said:


> Thanks man. I'm looking at a Panasonic Whispersync. It's DC so you can't use a dinner switch on it.
> 
> I may end up just putting two 200cfm in instead, so I can run one or both depending on how many people are in the room. Any thoughts there?


I can't speak to how much air flow you need but I used this method at first in my smoking room (with a stacked rocker switch) and it worked as I planned. The negative I found was that they get gunked up pulling smoky air threw them and those types of fans are not usually easy to clean. I stopped using that method because of that and it was impossible to keep the room cooled in 100 deg.+ weather running a total loss exhaust.


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## StogieNinja (Jul 29, 2009)

Johnpaul said:


> I can't speak to how much air flow you need but I used this method at first in my smoking room (with a stacked rocker switch) and it worked as I planned. The negative I found was that they get gunked up pulling smoky air threw them and those types of fans are not usually easy to clean. I stopped using that method because of that and it was impossible to keep the room cooled in 100 deg.+ weather running a total loss exhaust.


How frequently were you using them, and how long did it take to gunk up? I only smoke twice a week max, so I'd be looking at using it maybe 75 times a year for a couple hours at most (I smoke outside in the summer time)

Also, what are you running now? I'd be interested to hear your setup. I've read several things about CFM and how big or small the fan should be, but haven't really gotten feedback on long-term success (or lack thereof). Never thought about the fans being gunked up as a problem...


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## Johnpaul (Aug 15, 2011)

Aninjaforallseasons said:


> How frequently were you using them, and how long did it take to gunk up? I only smoke twice a week max, so I'd be looking at using it maybe 75 times a year for a couple hours at most (I smoke outside in the summer time)
> 
> Also, what are you running now? I'd be interested to hear your setup. I've read several things about CFM and how big or small the fan should be, but haven't really gotten feedback on long-term success (or lack thereof). Never thought about the fans being gunked up as a problem...


I smoke a lot, usually three a day, so I probably had mine on maybe 6-8 hours a day. I only used them for about three months but when I removed them they had a film of tar (or whatever yellow smoke stuff is) and dust sticking to that. It may work fine in your situation, but it was clear to me that it would be an issue for me.

Currently I have a 16x24 intake register installed in the ceiling with a 3M Filtrete 1500 filter. Behind that I have a Phresh carbon filter (I originally had a cheap Vantech? brand but it was not very good) and a 6" 190cfm inline fan that then runs back to two return registers in the room. With just me smoking the system works okay (not great) but could really use more cfm because it can get a little smokey sometimes. I am very happy with the filtering portion of my system, I think I just underestimated the flow I needed.

I should also note that because my current fan is having to suck air threw two filers, and its a budget unit, I highly doubt I am actually running the 190cfm it's rated at.


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## StogieNinja (Jul 29, 2009)

Johnpaul said:


> I smoke a lot, usually three a day, so I probably had mine on maybe 6-8 hours a day. I only used them for about three months but when I removed them they had a film of tar (or whatever yellow smoke stuff is) and dust sticking to that. It may work fine in your situation, but it was clear to me that it would be an issue for me.
> 
> Currently I have a 16x24 intake register installed in the ceiling with a 3M Filtrete 1500 filter. Behind that I have a Phresh carbon filter (I originally had a cheap Vantech? brand but it was not very good) and a 6" 190cfm inline fan that then runs back to two return registers in the room. With just me smoking the system works okay (not great) but could really use more cfm because it can get a little smokey sometimes. I am very happy with the filtering portion of my system, I think I just underestimated the flow I needed.
> 
> I should also note that because my current fan is having to suck air threw two filers, and its a budget unit, I highly doubt I am actually running the 190cfm it's rated at.


So you're basically filtering the air and pumping it back into the room, then? Any reason you decided not to bring in outside air?


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## Johnpaul (Aug 15, 2011)

Aninjaforallseasons said:


> So you're basically filtering the air and pumping it back into the room, then? Any reason you decided not to bring in outside air?


That is exactly what I am doing. The reasons are to cut costs on heating and cooling (I live with very long and hot summers in California's central valley) and so I don't get complains from my roommates and neighbors of the cigar smell outside. I do keep the window open so there is some fresh air coming in most of the time.


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## cion (Mar 18, 2015)

quo155 said:


> Hey Cion! For your room size and location, I'd shoot for 700cfm exhaust, minimum.
> 
> 1. The 1500+ really is overkill, IMHO and I'd keep it between 700cfm and 900cfm...as long as the number is more than whatever you decide to feed into the room. A speed regulator is a great idea!
> 
> ...


Hello Tommy thanks for your input, so you say you would go for a MINIMUM off 700CFM but 1,500 CFM is overkill. What do you think would be that magic number then? I'm looking at three ultra quiet 280CFM fans, totalling 840. Do you think that would DEFINITELY do it or should I go 1000CFM?

So you believe I should buy a fan to PULL air back into the room, but keep it below the CFM going out...

So, you don't believe just having an open vent to outside would be enough with the exhaust pulling air out? I thought it the exhaust fan would cause a negative pressure, and would pull air from anywhere it can get it...that would be that open direct vent...wouldn't it?

Tommy you didn't answer this...I'm curious to your thoughts (below)

I've seen photos of the exhaust and fresh air intake side by side on the outside of the house in others cigar room. Doesn't that defeat the purpose of a fresh air intake? Wouldn't the intake pull the cigar smoke from the exhaust right back in? (photo below)









You said not to buy a duct heater because you believe I would have sufficient heat with the baseboards and electric fire place, but you don't think the room would get cold in this up north 10-20 degree winters air blowing directly into the room?

I'm sorry If I'm asking the same questions or questioning certain things you answered, I just want to be sure, and I want to order everything today.

Thanks Tommy I really appreciate your opinion/facts!


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## cion (Mar 18, 2015)

Ok, This is the HVAC blueprint I came up with based on the advice I have got from various sources including this as well as other threads here and abroad. Tell me what you guys think. I'm planning on ordering the various fans etc. later today so all input would be greatly appreciated. Thank you!


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## quo155 (Aug 10, 2010)

I may be late at answering (& if I am, I'm sorry!)...



cion said:


> Hello Tommy thanks for your input, so you say you would go for a MINIMUM off 700CFM but 1,500 CFM is overkill. What do you think would be that magic number then? I'm looking at three ultra quiet 280CFM fans, totalling 840. Do you think that would DEFINITELY do it or should I go 1000CFM?


I think the 840cfm will work perfectly, go for it!



cion said:


> So you believe I should buy a fan to PULL air back into the room, but keep it below the CFM going out...





cion said:


> So, you don't believe just having an open vent to outside would be enough with the exhaust pulling air out? I thought it the exhaust fan would cause a negative pressure, and would pull air from anywhere it can get it...that would be that open direct vent...wouldn't it?





cion said:


> You said not to buy a duct heater because you believe I would have sufficient heat with the baseboards and electric fire place, but you don't think the room would get cold in this up north 10-20 degree winters air blowing directly into the room?


Yes...I did, but I've not sat and looked over this with my engineering hat as I should have...I would pull fresh air in, BUT...you're right in that it would be cold air during Winter. If you have air that is able to come into the room from other areas, under door(s), etc...in which I am sure you do, then you may not need the outside to inside air fan. Thus, not needing a duct heater. If you do pull in outside air, just to have it as an option (it really helps "flush" out the room _quicker_...then I'd recommend the duct heater.



cion said:


> Tommy you didn't answer this...I'm curious to your thoughts (below)
> 
> I've seen photos of the exhaust and fresh air intake side by side on the outside of the house in others cigar room. Doesn't that defeat the purpose of a fresh air intake? Wouldn't the intake pull the cigar smoke from the exhaust right back in? (photo below)


You are correct and I would never recommend the two be close! If you can put on different sides of the room (if two exterior walls), then please do...or at the least, try and separate as much as possible. But, this will only apply if you are bringing in outside air.



cion said:


> I'm sorry If I'm asking the same questions or questioning certain things you answered, I just want to be sure, and I want to order everything today.


You are fine, ask away. However, it looks like you may have already ordered stuff and if so, I am sorry for my delay in getting back to you. I don't frequent this forum anymore and I only log in to see if you've needed anything else! I just hope I was able to help you in some way...and not confuse you!

-Tommy


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## quo155 (Aug 10, 2010)

cion said:


> Ok, This is the HVAC blueprint I came up with based on the advice I have got from various sources including this as well as other threads here and abroad. Tell me what you guys think. I'm planning on ordering the various fans etc. later today so all input would be greatly appreciated. Thank you!


Great drawing and it looks like you've got it figured out. I know the task can be challenging and such, but it will be _so worth it_ in the end!


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## cion (Mar 18, 2015)

quo155 said:


> Great drawing and it looks like you've got it figured out. I know the task can be challenging and such, but it will be _so worth it_ in the end!


Thank you so much Tommy! (When ever you see this lol)

No you weren't late. I decided to wait a few days to get a response or two. I didn't want to get stuff and it wasn't correct. However between you and my carpenter okaying this setup I'm going to order the fans. Thank you again for answering all of my questions especially the one concerning the exhaust and intake being so close. I'm putting the exhaust and intake on separate sides of the house. The intake will go on the side of my house with windows and the exhaust will go to the side without windows (so my wife and tenant doesn't have to smell smoke when they have their windows open.) Thanks again Tom!


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## quo155 (Aug 10, 2010)

Cion, good to hear brother...and I wish you the best of luck with your build! 

You will have to continue to add photos to your Man Cave thread so I can check them out!


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## cion (Mar 18, 2015)

quo155 said:


> Cion, good to hear brother...and I wish you the best of luck with your build!
> 
> You will have to continue to add photos to your Man Cave thread so I can check them out!


Definitely will do!


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